Packaged semiconductor devices typically comprise a semiconductor die containing one or more semiconductor elements, external leads by which the device is to be coupled to the circuit in which it is intended to function, bonding wires or equivalent connecting the semiconductor element(s) to the external leads, and a housing or encapsulation surrounding the die and the bonding wires to provide environmental protection. Many different forms of packaged semiconductor devices are known and used, ranging from a simple two lead diode to complex integrated circuits having millions of transistors and hundreds of external leads.
It is common to mount packaged semiconductor devices on circuit boards. Circuit boards generally comprise an insulating substrate having thereon one or more layers of conductors to which the various semiconductor devices and other electronic components attach at various attachment locations. In order to facilitate the design and assembly of circuit boards, certain package shapes, sizes and lead arrangements have been registered as "JEDEC" standards. JEDEC stands for Joint Electron Device Engineering Council JEDEC registered package designs have pre-determined mechanical dimensions and lead arrangements. Examples of well known JEDEC standard package configurations are 14 to 40 lead dual-in-line (DIL) packages, TO-3, TO-218 and TO-220 packages. The availability of a wide variety of semiconductor devices or functions in JEDEC standard package configurations greatly facilitates circuit board design because the device footprint on the circuit board is known from the JEDEC standard and does not depend on the particular manufacturer or the electrical function of the packaged device.
Many different types of power semiconductor devices are produced in JEDEC standard package configurations. As used herein, the words "power device" and "power semiconductor device" are intended to refer to devices composed of one or more electronic elements, wherein the device generally dissipates .gtoreq. 10 watts or carries a current of .gtoreq. 1 amp and blocks voltages of .gtoreq. 40 volts.
Frequently it is necessary to use multiple power devices to accomplish a particular electrical function. This is especially common in motor control circuits and multiple solenoid drivers where two to six or more power semiconductor devices may be required to drive a fractional horsepower variable speed motor or individual inductive loads. The rapid adoption of electronic controls and actuators in automotive and white goods applications has stimulated the use of multiple power device circuits for controls and switches. Historically, such circuits have been implemented by mounting the required number of power devices individually on the circuit board where they are interconnected into the desired electrical function. However, as the usage of multi-device control or driver circuits increases it becomes more desirable to have pre-packaged modules or sub-assemblies in which the individual power semiconductor devices are already grouped together since this simplifies circuit board construction.
One solution to the need for multiple device sub-assemblies has been to provide the multiple devices on a single semiconductor chip. This arrangement works well for low power applications (e.g., a few watts or less), as in conventional integrated circuits where individual active device areas are comparatively small and voltage and currents are low, but is not suitable for power device applications. This is because power devices generally require much larger active areas. lt is well known that the cost of semiconductor devices increases very rapidly with device active area. For example, if it costs $ 4.times. to make four individual power transistors on separate die, it may cost $ .gtoreq. 40.times. to make a single semiconductor die with the same four power transistors thereon. A further difficulty with integrating multiple power devices on a single semiconductor chip is that it becomes much more difficult to provide electrical isolation between the devices, which is often necessary in multi-device control circuits where the multiple semiconductor devices do not operate in parallel.
Another approach that has been used in the prior art is to mount individual semiconductor die on a common support, connect them together and/or to external leads and then enclose the combination in a protective encapsulation. While this procedure is successful and widely used it suffers.from a number of drawbacks well known in the art. For example, it is frequently impossible to provide a full functional test of the power semiconductor chip before it is assembled onto the common support. As a result, if the functional test of the assembled module shows that a particular die is defective, either the entire module must be discarded or the defective chip removed and replaced and the assembly re-tested. Such repair is usually a "by-hand" operation and is comparatively very expensive.
Thus, there continues to be a need for improved, low cost power device modules which are convenient to use. It is especially desirable to have modules whose footprint conforms to a JEDEC standard footprint so that custom circuit board mounting configurations are avoided.